A major problem of past and present keratoprostheses has been collagen dissolution at the cornea-alloplastic junction. This leads to loosening and extrusion of the prosthesis. ProplastR, a fibrous carbon-teflon material, has been used to stabilize other body prostheses because tissue invades the Proplast obliterating the tissue-prosthesis interface. This material is well incorporated into the cornea in rabbits and cats. In the initial work under this grant, a prosthesis was developed and modified so that when it is implanted in cat corneas it becomes well incorporated with very low incidence of leak or extrusion. Cats have retained these prostheses for over one year. Problems with the prosthesis include a tendency for the conjunctiva to cover the optical core once the core is exposed. Another problem is the retroprosthesis membrane which forms following the implant. The proposed research is to implant prostheses with optical cores which protrude 0.5 to 0.7mm above the prosthesis rim and 0.5mm into the anterior chamber to prevent closure of the conjunctiva over the core and inhibit the occurrence of retroprosthesis membranes. Other techniques such as change of core material and the incorporation of a flange barrier to conjunctival migration will be tried if increasing core elevation is not successful. When retroprosthesis membranes form, discission and suction cutter removal will be evaluated. Eyes will be removed and studied histologically at three, six, nine and 12 month intervals after exposure of the prosthesis.